textium: Rect: add gl_bottom()

textium/src/geometry.rs

@@ -39,9 +39,12 @@ impl<T> Rect<T>
     /// Return the position of the left edge of the rectangle.
     #[inline(always)]
     pub fn left(&self) -> T {self.x}
-    /// Return the position of the bottom edge of the rectangle.
+    /// Return the position of the bottom edge of the rectangle (coord system with 0 at top).
     #[inline(always)]
     pub fn bottom(&self) -> T {self.y + self.h}
+    /// Return the position of the bottom edge of the rectangle (gl/mathematical coord system).
+    #[inline(always)]
+    pub fn gl_bottom(&self) -> T {self.y - self.h}
     /// Return the position of the right edge of the rectangle.
     #[inline(always)]
     pub fn right(&self) -> T {self.x + self.w}